The public health importance of root surface caries has increased due to people's increased longevity of life and retention of teeth. The restoration of root surface caries continues to be problematic, with few published clinical studies and few guidelines having been established. Although topical fluorides are clearly effective in the control of coronal caries, their efficacy in the management of root caries has not been well elucidated. Few clinical studies have investigated the use of topical fluorides in the prevention and treatment of root caries. No randomized clinical trials have been reported on the treatment of incipient root caries with topical fluoride vs. placebo. The purpose of this study is to develop and pilot the methodology to be used in a subsequent, larger, randomized, clinical trial to evaluate the efficacy of 0.4% SnF2 gel in the reversal and prevention of incipient root caries lesions. Aspects to be piloted include the methodology for measurement of lesion dimensions, the efficacy of agents essential for the calculation of sample sizes, and the methodology for assessment of relationships between salivary flow, buffering capacity, salivary fluoride, and microbiological findings and the reversal/progression of incipient root lesions. Forty individuals with incipient root caries will be randomly assigned to two treatment groups: 0.4% SnF2 gel and placebo gel. Subjects will be recalled at 6, 12, and 18 months and evaluated blindly. The findings will be invaluable in the planning of the subsequent larger clinical trial to help determine whether 0.4% SnF2 gel should be recommended for root caries reversal based on scientific evidence. If found effective, this agent will reduce the need for invasive, and often unsuccessful, restoration of root surface caries.